The present invention relates to a microphone-array apparatus which selectively receives an acoustic signal through use of a plurality of microphone elements and a method for extracting a desired signal with the apparatus.
When a desired acoustic signal (hereinafter referred to as the desired signal) is received by a microphone, undesired acoustic signals, such as machinery noises, unnecessary voices and so on (hereinafter referred to as the noise) are simultaneously received, causing a reduction of the SN ratio, the occurrence of howling and so forth in many cases. The solution of this phenomenon has been an important problem in a loudspeaking telephone system, a PA (Public Address) system and the like. To settle this problem, a directional microphone has been employed in many cases. In practice, however, this method poses many problems, such as limitations on the talker's position and noise source positions according to the direction of the microphone because of its fixed directivity pattern. In recent years, a linear microphone-array has been employed with regard to achieving sharp directivity (R. L. Wallance et al, U.S. Pat. No. 4,311,874, issued on Jan. 19, 1982). With this method, however, since the design theory is limited specifically to the plane wave, the operation does not agree with the theory when sound waves are spherical waves as in many actual cases and, in addition, a microphone-array as long as one to several meters is needed.